<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div class="text-area">
      <span>F</span>
      <span>o</span>
      <span>l</span>
      <span>l</span>
      <span>0</span>
      <span>w</span>
      <span>m</span>
      <span>e</span>
    </div>
  </body>
  <style>
    * {
      padding: 0;
      margin: 0;
    }
    .text-area {
      display: flex;
      height: 100px;
      justify-content: space-around;
    }
    .text-area span {
      animation: shadowing 1s ease-in-out infinite alternate;
      color: #f00;
      font-size: 40px;
    }
    @keyframes shadowing {
      to {
        color: #ff0;
      }
    }

    span:nth-child(n + 2) {
      animation-duration: 0.2s;
    }
    span:nth-child(n + 3) {
      animation-duration: 0.4s;
    }
    span:nth-child(n + 4) {
      animation-duration: 0.6s;
    }
    span:nth-child(n + 5) {
      animation-duration: 0.8s;
    }
    span:nth-child(n + 6) {
      animation-duration: 0s;
    }
  </style>
</html>
